The invention concerns silver-doped vanadium pentoxide antistatic agents in general, and in particular, a method for preparing the antistatic agent at room temperature and recovering a product with minimal precipitates.
The preparation and use of vanadium pentoxide is of interest in the manufacture of radiation sensitive elements in general and to the photographic industry in particular. For example, U.S. Pat. No. 4,203,769 describes the preparation of a material suitable for use as an antistat in radiation-sensitive elements in general and photographic products in particular. The preparation involves forming a melt comprised of at least 80% by weight of vanadium pentoxide and casting the melt into a solubilizing amount of water. The resultant product may be euphemistically referred to as xe2x80x9cVanadium Oxidexe2x80x9d, xe2x80x9cgelled (or hydrated) Vanadium Oxidexe2x80x9d, xe2x80x9ccolloidal vanadium oxidexe2x80x9d or V2O5 (the chemical composition of divanadium pentoxide) but, in truth, the precise composition is unknown. It has the physical form of microscopic fibers that have been referred to as xe2x80x9cliving polymersxe2x80x9d because their compositions and properties have been observed to change with time. This preparation will herein be referred to as the xe2x80x9cmelt-quenchedxe2x80x9d preparation.
In U.S. Pat. Nos. 5,455,153 and 5,654,089, Gardner describes the use of various polyester resins to xe2x80x9cprotectxe2x80x9d vanadium pentoxide fibers prepared using the xe2x80x9cmelt-quenchedxe2x80x9d method. Gardner claims the cladding of V2O5 doped with silver wherein the silver doping is achieved by including silver oxide (Ag2O) in the original melt. The described process for doping is a high temperature process that produces a metastable product of unknown composition, but with antistat properties that are important in the manufacture of photographic products. The antistat properties were observed to vary with the level of silver doping. The process results in the production of undesirable particulate matter as a by-product that must be subsequently removed. This method of preparing melt-quenched, silver doped, vanadium oxide colloidal gels will herein be referred to as the xe2x80x9cmelt-quenched, silver doped, vanadium oxide preparation.
Coustier, Passerini, and Smyrl (see, F. Coustier, S. Passerini, and W. H. Smyrl, xe2x80x9cDip-Coated Silver-Doped V2O5 Xerogels as Host Materials for Lithium Intercalation,xe2x80x9d Solid State Ionics, 100 (1997) 247-258) and Coustier, Hill, Owens, Passerini, and Smyrl (See, Fabric Coustier, Jason Hill, Boone B. Owens, Stefano Passerini, and William H. Smyrl, xe2x80x9cDoped Vanadium Oxides as Host Materials for Lithium Intercalation,xe2x80x9d Journal of The Electrochemical Society, 146(1999)1355-1360) disclose a method for doping colloidal vanadium oxide gel using a low temperature technique. Vanadium oxide colloid is initially prepared by a xe2x80x9csol-gelxe2x80x9d technique that has been described by Livage, in a review of colloidal vanadium oxide gels (See, Livage, xe2x80x9cVanadium Pentoxide Gels,xe2x80x9d Chem Mater., 3(1991)578-593.
Livage""s review covers both the high temperature xe2x80x9cmelt-quenchedxe2x80x9d preparations as well as the xe2x80x9csol-gelxe2x80x9d technique. The xe2x80x9csol-gelxe2x80x9d technique has been described as the xe2x80x9cprotonation of sodium metavanadate solutionxe2x80x9d. The prior art teaches that properties desirable for use as cathodes in batteries can be achieved by metallic silver doping of xe2x80x9csol-gelxe2x80x9d prepared colloidal vanadium oxide gels.
The art does not suggest nor give incentive to believe that whatever gel is prepared using the xe2x80x9csol-gelxe2x80x9d technique would have the same desirable properties (for example, those required in photography) as gels prepared using the high temperature xe2x80x9cmelt-quenchedxe2x80x9d preparation method. In fact, the two techniques don""t even begin with the same starting materialsxe2x80x94sodium metavanadate in one case, vanadium pentoxide in the other. Furthermore, the doping of vanadium pentoxide, as studied in the two Coustier references above, is for an application totally different from photography or imaging; and therefore Coustier et al. might wish to achieve totally different properties. Coustier et al. was interested in producing a material suitable for use as cathodes in high-capacity lithium batteries. That method would not predictably produce an antistat material suitable for use in photographic/imaging elements.
Hence, it remains uncertain to one skilled in the art what properties would result from doping the analogous xe2x80x9cmelt-quenchedxe2x80x9d vanadium oxide gel material with metallic silver at low temperatures. No prior art teaches, or even predicts, that properties desirable for use as antistat materials in photographic elements would be achieved by metallic silver doping of xe2x80x9cmelt-quenchedxe2x80x9d colloidal vanadium oxide gels at any temperature. Neither does the prior art teach or suggest that the material prepared using the sol gel prepared starting material for cathodes in high-capacity lithium batteries would be suitable as an antistat in the imaging arts.
In making antistat materials, three improvements would be desirable: 1.) A room temperature technique for silver doping is desired that would provide a stable product of known composition; 2.) The silver/vanadium ratio should be adjustable to meet the requirements for particular applications; and 3.) The final product should be free of particulate matter. The resultant product should be useful as antistat material in photographic or imaging elements as described in U.S. Pat. Nos. 5,709,985; 6,010,836; and 6,013,427.
It would be useful in the technology to have a method of doping xe2x80x9cmelt-quenchedxe2x80x9d colloidal vanadium gel with colloidal silver at room temperature to produce an antistat useful in the imaging arts.
The present invention discloses a method of doping xe2x80x9cmelt-quenchedxe2x80x9d colloidal vanadium gel with colloidal silver. Unexpectedly, the method yields a product that is stable, adjustable, and free from particulate matter.
The present invention discloses: A method of doping vanadium pentoxide with silver comprising the steps of:
a. providing vanadium pentoxide gel;
b. providing stable colloidal silver; and
c. combining the vanadium pentoxide gel and the colloidal silver at room temperature for a period sufficient for vanadium (+5) to be electrochemically reduced to vanadium (+4) and for silver to be oxidized (+1).